#include<bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

const int Z = 5000000;
bool sieve[Z + 1];
int X[Z + 2];

int main() {
    sieve[0] = sieve[1] = true;
    for (int i = 2; i <= 3000; i++) {
        if (sieve[i]) continue;
        for (int j = i * i; j <= Z; j += i) sieve[j] = true;
    }

    rep(i, Z + 1) {
        if (sieve[i]) continue;
        int p = i;
        while (p) { X[i] |= (1 << (p % 10)); p /= 10; }
    }

    int N, V; cin >> N; V = 0;
    while (N--) { int a; cin >> a; V |= (1 << a); }
    rep(i, Z + 1) if (X[i] & ~V) X[i] = -1;
    X[0] = -1; X[Z + 1] = -1;

    int ans = -1;
    for (int i = 1; i <= Z + 1; i++) {
        if (X[i] != -1) continue;
        int tmp = 0, len = 0;;
        for (int j = i - 1; X[j] != -1; j--) { tmp |= X[j]; len++; }
        if (tmp == V) ans = max(ans, len - 1);
    }

    cout << ans << endl;

    return 0;
}